Description

NaN is typically used in JavaScript as the return value of a numeric operation when an argument is invalid or conversion fails. For example, 0/0 and Math.sqrt(-1) both return NaN. So do Number("xyzzy") and Math.sin("Frank"). While the IEEE standard defines many NaN bit-patterns, they are indistinguishable in JavaScript, so in effect there's only one NaN.

NaN is not equal to any other value. In fact, it is not even equal to itself: if x is NaN, then x != x.